1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine.
2. Description of the Related Art
In Japanese Unexamined Patent Publication No. 3-78562, the injection hole of a fuel injector is formed as a slit. The injection hole has a height which is relatively small and is nearly uniform, and has a width which is gradually narrowed inward at a predetermined contained angle. Therefore, the injected fuel assumes the form of a flat triangular spray having a relatively small thickness. In the fuel spray of such a triangular shape, almost all fuel comes into sufficient contact with the air and is favorably atomized. The injection hole is directly communicated with the fuel reservoir on the downstream side of the seat portion of the valve body. The fuel is injected through the injection hole as the pressure of fuel in the fuel reservoir is increased.
In the above-mentioned fuel injector, the contained angle of the triangular fuel spray is limited by the contained angle of the injection hole, and the amount of fuel injected with the triangular fuel spray per unit time, i.e., the flow rate of the fuel, is limited by the area of the injection hole which is opened to the fuel reservoir since the injection hole is directly communicated with the fuel reservoir. In this fuel injector, when the contained angle of the injection hole is increased, the area of the injection hole opened to the fuel reservoir increases and thus the flow rate of the fuel increases. Conversely when the contained angle of the injection hole is decreased, the area of the injection hole opened to the fuel reservoir decreases and thus the flow rate of the fuel decreases.
In the above-mentioned fuel injector, therefore, the area of the injection hole opened to the fuel reservoir is set such that a desired flow rate of the fuel is realized, and then the contained angle of the injection hole is set such that the opening area is realized. Due to tolerance in the machining and the like, however, it is difficult to provide the contained angle of the injection hole as desired. Even a small difference between the contained angle of the injection hole that is provided and the desired contained angle makes it difficult to realize the desired area of the injection hole opened to the fuel reservoir. Therefore, a desired flow rate of the fuel with the triangular fuel spray cannot be realized.